The present invention relates to the field of devices for remote control of movement. More particularly, the invention concerns a single device for remote control of elements, particularly gripping elements, such as articulated jaws or fingers and adapted to converge upon the object to be gripped.
The invention is particularly applicable to the control of an element having to be placed successively in active position, position in which the element is blocked, then disengaged from this blocked active position, the control of the cycle being permitted from one sole movement transmission means, with unidirectional linear or angular action. The same manoeuvre of the transmission means makes it possible, when the controlled element is inactive, to take it towards its blocked active position, and when the controlled element is in blocked active position, a fresh manoeuvre identical to the preceding one returns it towards its inactive starting position.
The invention is particularly applicable to the control of elements for gripping and displacing objects, forming an artificial hand usable for the remote manipulation of objects in an aggressive or dangerous environment; the invention will also be more particularly applicable to the production of a manual prosthesis controlled by cable, for example from a scapular or dorsal harness and transmitting to the articulated fingers an effort of traction taking the fingers towards their gripping position. It is in connection with this latter application that the invention will be described hereinafter, although it does not constitute the limiting framework of application of the device described and claimed here. The latter may in effect be adapted to the control of numerous bistable systems moving between two positions of rest, the same unidirectional manoeuvre of a single transmission means operating the passage from one position to the other.
Numerous systems of manual prostheses are known, aiming at allowing persons having undergone an amputation of the hand, to perform certain gestures or certain elementary functions of everyday life, both personal and social, and in particular and especially the bi- or pluridigital gripping of objects, under conditions reproducing more or less faithfully the gripping functions of the natural hand.
French Patents Nos. 73 25719, 83 15850 and 90 10455 for example disclose a hand prosthesis constituted by a rigid plate forming palm supporting articulated elements forming the phalanxes, the latter being provided with an inner spring made of elastically deformable material and returning the corresponding finger in position of extension, a terminal cable connected to the end of each finger being adapted to provoke the movement of angular closure of the finger; the terminal cables are connected to a common beam or bar distributing the traction transferred successivly on each of the terminal cables, this traction coming from a single cable controlled by the user, for example from a dorsal harness. This mechanical structure is completed by a surfacing or trim both for facing and functional, viz. a rigid or semi-rigid dorsal shell and a coating made of supple material, particularly cellular on the palm face.
The invention relates to a device for transmitting and controlling the effort of traction operating from the single cable and driving terminal cables for individual control of the fingers belonging to a manual prosthesis, in particular of the type such as provided by the above-mentioned Patents; reference is expressly made to these Patents for a more complete description of the elements ensuring the functionality and the aesthetically satisfactory aspect of the prosthesis.
According to Patents 83 15850 and 90 10455, a device has been provided for locking the traction arriving at the beam for balancing and distribution on the terminal cables. The object of the devices provided in these Patents is to make it possible to block the gripping elements, particularly the fingers once closed on the object gripped; such blocking allows comfort of use in that it allows a relaxing of the effort of traction having controlled the retraction of the fingers and the grip of the object. Thus the user may, without maintaining his/her effort, conserve in manually held position the gripped object which is in that case capable of being displaced or changed in its positioning in space. In effect, it will be understood that it is particularly hard and difficult for the user to ensure at the same time the maintaining of a traction ensuring stability of the grip and, in parallel, a manipulation or a manoeuvre of the object held in the hand.
The mechanical blocking devices according to the afore-mentioned Patents employ elements acting on the traction cable, either directly by pinching or braking, or via means associated with the cable and subjected to a locking catch. In this way an immobilization of the cable in the position of the closed fingers in abutment on the object is obtained, despite the stop of any traction voluntarily controlled by the user on the cable. Despite their interest and efficiency, these known devices remain imperfect. In effect, although their actuation towards the blocking position can be controlled automatically, for example by a return spring controlling the displacement towards its active position of the locking catch constituted by a pawl associated with a rack or a ratchet wheel, unblocking of the locking system requires a specific manoeuvre and an intervention of the other hand, which handicaps and slows down the overall operation of the ongoing manipulation.
A first object of the invention is to provide a system for locking the hand in position where the fingers are closed on the gripped object, which locking automatically occurs at the end of the phase of closure, the fingers having arrived in position of abutment on the gripped object; this system allows a relaxing of the voluntary effort of traction, while ensuring maintenance of the gripping position acquired.
A second object of the invention is to allow an unlocking which occurs when the user desires, therefore at the opportune moment, solely by manoeuvring the traction cable, while allowing the user to resume, at the moment of release of the fingers, the control of the gripping position previously set. More especially according to this object of the invention, after a period of rest of the traction cable, the maintained grip no longer being under the voluntary control of the user, the latter can in one and the same manoeuvre return to the gripping position voluntarily controlled by the traction cable via an autonomous action of unlocking of the gripping elements, by means of a single subsequent action on the single cable.
Another object of the invention is to introduce in the functioning of the artificial hand a comfort and convenience of control such as a precision of the gesture, by an effect of demultiplication of the movement between the movement of control and the displacement of the remote-controlled elements.
Finally, an essential object of the invention is to allow the use of a single movement control means, for example a linear traction means, to take a bistable element successively towards an active position, position stable and blocked therefore allowing relaxing of the effort, then subsequently by the same manoeuvre as the preceding one, to disengage the element from this active position and control the progressive and controlled return of the element towards its inactive, stable starting position.
To that end, the invention relates to a device for remote-control by a single manoeuvre of at least one element such as a gripping element formed by articulated elements and adapted to close, converging upon the object to be gripped, the device ensuring a blocking of said elements in their active position, while allowing in this stable position a relaxing of the control manoeuvre, characterized in that it comprises:
a) a rotating element such as a primary pulley connected to a control means such as a cable wound and driven in rotation by the traction of said cable;
b) a spring returning the pulley towards its initial position against the action of said cable;
c) a secondary pulley connected to the end of an output cable, this latter terminating by its opposite end at the gripping elements;
d) disengageable mechanical drive means transmitting the torque from the primary pulley towards the secondary pulley;
e) means for blocking the secondary pulley, adapted to immobilize the secondary pulley for a predetermined value of said torque, corresponding to the active position.
According to a more particular form of embodiment, the primary pulley and the secondary pulley are arranged on a common shaft, and the disengageable drive means are constituted by two discs, viz. a driving disc fast in rotation with the primary pulley and a driven disc fast in rotation with the secondary pulley, the discs presenting on each of their opposite faces surface unevenness, adapted to ensure, upon contact of the two discs by their opposite faces, the drive of the disc driven by the driving disc.
More especially, within the framework of this embodiment, the opposite faces of the respectively driving and driven discs comprise asymmetrical teeth forming on one side of the tooth an inclined plane forming a cam, the teeth being regularly distributed over the periphery of each disc and being separated by hollow housings of complementary profile, allowing the engagement of the teeth fast with a disc in the housings of the opposite disc when the two discs are in the engaged position, the slope of said inclined planes being such that, for values of the torque applied to the driving disc less than a determined threshold value, the two discs, driving and driven, are fast in rotation, while, for a torque attaining this critical value, further to the resistance opposed by the gripping elements having arrived in position of abutment on the object, said resistance transmitted by the output cable and the secondary pulley, the teeth of the driving disc slide freely on the teeth, then immobilized, of the driven disc, by their opposite inclined planes, which, by cam effect, provokes the axial translation of the secondary disc thus pushed by the driving disc towards the disengaged position of the drive means.
In particular, the inclined planes of the teeth of the driving disc slope downwards in the direction of rotation of the driving disc in action for the gripping manoeuvre, while the inclined planes of the teeth of the driven disc slope upwards in the direction of this same rotation, all these inclined planes being of the same angle and being opposite and thus being in contact from one disc to the other, when the drive means are in the engaged position.
According to another characteristic, the teeth of the discs comprise at their apex a flat portion, defining for each tooth a planar face parallel to the mean plane of the discs and forming a foundation for rest of the flat portion of the tooth located opposite, when the drive means are in disengaged position.
Advantageously, the side of each tooth opposite the inclined plane is orthogonal with respect to the plane of the disc, each tooth thus having a rectangular trapezoidal section.
According to an advantageous embodiment of the invention, the secondary pulley and the driven disc form a one-piece assembly, the driven disc being formed by a cheek of the secondary pulley, oriented towards the driving disc, being thereopposite.
Likewise, the secondary pulley is associated with a return spring, such as a helicoidal spring surrounding said shaft and adapted to return the secondary pulley towards its position of abutment, by its cheek forming driven disc, on the driving disc.
The element for blocking the secondary pulley in the position of gripping of the gripping elements is in particular constituted by a ring facing the cheek of the secondary pulley opposite the cheek in contact with the driving disc. This locking ring, on the one hand, and the opposite cheek of the secondary pulley, on the other hand, comprise surfaces provided with unevenness cooperating together from one face to the other in order to ensure blockage of the pulley in position, when the latter is brought into contact with said ring by the axial thrust undergone from the driving disc during the phase of slide of the teeth of the driving disc rising and pushing the inclined planes of the driven disc fast with the secondary pulley; to that end, the locking ring is provided at a distance from the secondary pulley equal to or less than the height of the trapezium formed by each of the teeth of the driving disc, said height corresponding to the axial stroke of translation of the secondary pulley, under the thrust of the teeth forming cams of the driving disc, in order to come into contact with the locking ring.
The flat portions located at the apex of the teeth comprise, at least on the driven disc, and preferably in the vicinity of the right angle starting the orthogonal side of the tooth, a projecting boss forming stop for the opposite tooth fast with the driving disc, this stop making it possible to mark and make aware for the user the mutual positioning of the teeth in disengaged position of the drive and of blocking of the secondary pulley, this boss being, in addition, of such section and height as to allow the tooth fast with the driving disc to surmount it and pass beyond, dropping in the following housing of the driven disc, when the torque exerted by the driving disc has gone beyond said critical threshold.
The mechanical transmission between the primary pulley and the driving disc is effected via a hub mounted for unidirectional rotation on the shaft of the device via a ratchet wheel and pawl assembly of the so-called xe2x80x9cfree wheelxe2x80x9d type, adapted to ensure drive in rotation of the driving disc by the primary pulley in the direction of rotation corresponding to the transmission of the effort of traction on the traction cable, the driving disc being disconnected from the primary pulley upon rearward return of the latter under the action of its return spring, ensuring rewinding of the primary cable on its receiving primary pulley, without action on the driving disc.
The ring locking the secondary pulley is also mounted for unidirectional rotation by a ratchet and pawl assembly of the xe2x80x9cfree wheelxe2x80x9d type, allowing a rotation of the ring with the secondary pulley in the direction of winding of the output cable and opposing any reverse rotation with rearward return of the output cable and gripping elements. The latter are thus blocked in this set position of equilibrium, by abutment of the secondary pulley on the locking ring, until a fresh traction from the cable generates the excess rotation of the driving disc, beyond this position of equilibrium, and provokes the return of the teeth of the driving disc in the next housings of the driven disc. This fresh mutual engagement of the teeth on the two discs provoking the axial translation of the secondary pulley under the thrust of its return spring, said pulley resuming its initial position of engagement on the driving disc via its cheek forming driven disc, and at the same time the secondary pulley then escapes from its engagement on the locking ring.
The groove for winding the traction cable on the primary pulley is provided with a radius greater than that of the groove for winding the output cable on the secondary pulley, thus allowing a demultiplication between the stroke of the traction cable and that of the output cable, the assembly constituting a pulley block allowing a greater precision in the control of the manoeuvre and a better yield of the effort in the gripping manoeuvre.
It may also be provided that the primary pulley comprises a recessed part on its periphery over a substantially semi-circular segment of crown, the non-recessed sector bearing on its periphery, substantially in a semi-circle, the groove for winding the traction cable, the central crown of the pulley comprising a plurality of regularly distributed housings for receiving the engagement of the end of a return spring working in torsion, the suitable choice of the housing possibly making it possible to calibrate the return force exerted on the primary pulley.
According to the preferred embodiment hereinabove, (the device) is inserted and contained in a housing provided with openings respectively for the traction and output cables, and the housing is mounted fast with a plate forming structure of an artificial hand, the output cable terminating, in manner known per se, in a single beam for distributing the traction on the terminal cables each serving a finger, each finger being able to be brought into bent position against the action of a spring, the traction cable being connected upstream to a manoeuvring harness worn by the user.